This invention relates to spark plugs for spark ignition type internal combustion engines, and more particularly to spark plugs having dual gaps.
In recent years, concerns have been increasing about environmental pollution due to exhaust gases discharged from automobiles and about the nursing of resources, and from this point of view spark plugs for use with internal combustion engines of automobiles have been increasingly required to be improved in performance. As countermeasures therefor, there has been proposed to enlarge a discharging gap as much as possible for the improvement of ignition performance, or to drop discharge voltage demand as much as possible for simplification of discharge devices, or to reduce changes in discharge voltage demand for increased reliability. However, these respective measures tend to be inconsistent with one another. More specifically, large discharge gaps necessitate high discharge voltages. On the other hand, thinner electrodes necessitate lower discharge voltages, but they are subject to severe consumption resulting in a large change of the discharge voltage with the passage time. In this regard, tips of electrodes can be made of gold or platinum which are hard to be consumed, but are costly.